Capacitor Basics and Detection
First, the basics
Capacitor is an energy storage component in the circuit for tuning, filtering, coupling, bypass, energy conversion and delay. Capacitor is usually called a capacitor.
Its structure can be divided into fixed capacitors, semi-variable capacitor, variable capacitor of three.
Capacitor Basics and Detection
1. Capacitance of the structure and characteristics of commonly used
Capacitor dielectric materials used can be divided according to their electrolytic capacitors, mica capacitors, ceramic capacitors, glass and enamel capacitance.
Table 1 Common features of the structure and capacitance
Capacitor capacitor structure and characteristics of the physical type of picture
Aluminum electrolytic capacitor is made of aluminum cylinder cathode, which is equipped with liquid electrolyte, insert a curved cathode made of aluminum do. Also need to deal after the DC voltage to the positive electrode to form a layer of dielectric oxide film to do. It is characterized by large capacity, but the leakage big, big error and poor stability, which are used in the exchange bypass and filtering, when used in less demanding signal coupling. Electrolytic capacitor has positive and negative distinction, can not be reversed when used. Have positive and negative polarity, when used, is not to take anti-negative.
Capacitor Basics and Detection
Paper dielectric capacitor with two electrodes made of metal foil, sandwiched in a thin capacitor paper, rolled into a cylindrical or flat cylindrical cores, and then sealed in metal shells or insulating material (such as wax, ceramics, glass, enamel, etc.) shell made. It is characterized by smaller and larger capacity can be done. But there are inherent inductance and loss was relatively large, more suitable for low frequency.
Capacitor Basics and Detection
Metallized paper dielectric capacitor structure and the same paper dielectric capacitors. It is a piece of paper, covered by a layer of metal film capacitors to replace the metal foil, small size, large capacity, normally used in low frequency circuits.
Oil paper dielectric capacitor paper dielectric capacitor which is immersed in the special treatment of oil, the pressure can enhance it. It is characterized by large capacitance, high pressure, but larger.
Capacitor Basics and Detection
Capacitor with glass glazing glass enamel for media, with the advantages of ceramic capacitors, and the smaller, high temperature.
Ceramic dielectric ceramic capacitor to do, spray both sides of the ceramic substrate of silver layer, and then firing the plate made of silver films do. It is characterized by small size, good heat resistance, low loss, high insulation resistance, but the capacity is small, suitable for high frequency circuit.
Ferroelectric ceramic capacitors have larger capacity, but the loss and temperature coefficient of larger, suitable for low frequency circuits.
Capacitor capacitor detection method based on knowledge and the basic knowledge and test method
Paper dielectric capacitor film capacitor structure and the same medium is polyester or polystyrene. Polyester film capacitors, high dielectric constant, small size, large capacity, good stability, suitable as bypass capacitors.
Polystyrene film capacitors, dielectric loss, high insulation resistance, but the temperature coefficient, can be used for high frequency circuit.
Capacitor capacitor detection method based on knowledge and the basic knowledge and test method
Mica capacitor with a metal foil or mica coating layer made of silver electrodes, a layer of laminated plate and the mica layer, then die in the bakelite powder or Cementing made in epoxy resin. It is characterized by a small dielectric loss, insulation resistance, temperature coefficient is small, suitable for high frequency circuit.
Capacitor Basics and Detection
Tantalum, niobium metal tantalum electrolytic capacitor is made or niobium cathode, with sulfuric acid solution to do so with the negative, with tantalum or niobium oxide film formed on the surface is made to do media. It is characterized by small size, high capacity, stable performance, long life, insulation resistance, good temperature characteristics. Used in demanding devices. Capacitor Basics and Detection
Semi-variable capacitor, also known as fine-tuning capacitor. It consists of two pieces of metal shrapnel or small groups, made the middle sandwiched media. Changes in regulation time or the distance between the two areas. It's media are air, ceramic, mica, film, etc.
It consists of a set of variable capacitor set pieces and a set of dynamic slices, and its capacity as the rotating action film can be continuously changed. The variable capacitor loaded with two coaxial rotation, called the double. Variable capacitor with air and polystyrene two kinds of media. Large volume of air dielectric variable capacitor, loss, multi-tube radios in use in the. Polystyrene dielectric variable capacitor made enclosed, small, multi-use in the transistor radio in.
2. Key performance indicators
Nominal capacity and allow the error: capacitor charge storage capacity, commonly used unit is F, uF, pF. Some capacitance capacitor superscript number is the nominal capacity of the capacitor. Capacitor's nominal capacity and its actual capacity would be error. Common fixed capacitance tolerances of the grade in Table 2. Nominal capacity fixed capacitor common line in Table 3. General, the capacitor directly write its capacity, is also useful to mark the digital capacity, usually in the capacity of less than 10000pF time to do with pF units, more than 10000pF when done with uF units. For simplicity, greater than 100pF and less than 1uF capacitor units often do not note. No decimal point, its unit is pF, a decimal point, and its unit is the uF. If the capacitor marked "332" (3300pF) 3 digits, left two yuan gives the capacitance of the first and second digit, while the third digit indicates the month in the post-add 0 number, the unit is pF.
Rated operating voltage: in the specified operating temperature range, long-term reliable capacitors work, it can withstand the maximum DC voltage is capacitor voltage, also known as the DC capacitor voltage. If the communication circuit, pay attention to the increase of the AC voltage can not exceed the maximum working voltage of DC capacitor. Common fixed capacitor voltage are 6.3V, 10V, 16V, 25V, 50V, 63V, 100V, 2500V, 400V, 500V, 630V, 1000V.
Table 2 used a fixed capacitance tolerances of other
Permissible error ± 2% ± 5% ± 10% ± 20% (+20% -30%) (+50% -20%) (+100% -10%)
Grade 02 Ⅰ Ⅱ Ⅲ Ⅳ Ⅴ Ⅵ
Table 3 used the nominal capacity of the fixed series capacitor
Capacitance range of categories of permissible error capacity of a nominal capacity of series
Paper dielectric capacitors, metallized paper dielectric capacitors, paper membrane capacitance of composite media, low frequency (a polar) organic thin film dielectric capacitor
5%
± 10%
± 20%
100pF-1uF 1.0 1.5 2.2 3.3 4.7 6.8
1uF-100uF 1 2 4 6 8 10 15 20 30
506,080,100
High frequency (polarity) organic thin film dielectric capacitors, ceramic capacitors, glass enamel capacitors, mica capacitors
5%
1pF-1uF
1.1 1.2 1.3 1.5 1.6 1.8 2.0
2.4 2.7 3.0 3.3 3.6 3.9 4.3
4.7 5.1 5.6 6.2 6.8 7.5 8.2 9.1
10% 1.0 1.2 1.5 1.8 2.2 2.7
3.3 3.9 4.7 5.6 6.8 8.2
20% 1.0 1.5 2.2 3.3 4.7 6.8
Aluminum, tantalum, niobium, titanium electrolytic capacitors 10%
± 20%
+50 / -20%
+100 / -10%
1uF-1000000uF 1.0 1.5 2.2 3.3 4.7 6.8
(Capacity of unit uF)
Insulation resistance: As capacitor dielectric between the two poles is not an absolute insulator, its resistance is not infinite, but a limited value, generally more than 1000 megohm, capacitor poles insulation resistance between the resistance is called, or called the leakage resistance , the size is under rated voltage DC voltage and leakage current through the capacitor ratio. Leakage resistance of the smaller, more serious leakage. Capacitor leakage will cause energy loss, this loss affects not only the capacitance of life, and will affect the circuit's work. Therefore, the bigger the better leakage resistance.
Dielectric loss: capacitors in electric field consume energy, usually loss of power and reactive power of capacitor ratio, that is, that the tangent of loss angle. The greater the loss angle, the greater the loss of the capacitor, the capacitor loss angle great work not suitable for high frequency cases.
Table 4, several common characteristics of capacitance
Capacity range of types of DC capacitor voltage (V) more than the magic l rate (MHz) the accuracy of leakage resistance (> MΩ)
Small paper dielectric capacitor 470pF-0.22uF 63-630 8 the following - Ⅲ> 5000
Metal shell sealed paper dielectric capacitor 0.01uF-10uF 250-1600 DC, pulse DC Ⅰ> - Ⅲ> 1000-5000
Small metal paper dielectric capacitor 0.01uF-0.22uF 160,250,400 8 The following Ⅰ> - Ⅲ> 2000
Metal shell sealed metallized paper dielectric capacitor 0.22uF-30uF 160-1600 DC, pulsating current Ⅰ> - Ⅲ> 30-5000
Film Capacitor 3pF-0.1uF 63-500 high-frequency, low frequency Ⅰ> - Ⅲ> 10000
Mica Capacitor 10pF-0.51uF 100-7000 75-250 the following 02 - Ⅲ> 10000
Ceramic Capacitor 1pF-0.1uF 63-630 low-frequency, high frequency 02 - Ⅲ> 10000
Aluminum Electrolytic Capacitor 1uF-10000uF 4-500 DC, pulse DC Ⅳ Ⅴ
Tantalum, niobium electrolytic capacitor 0.47uF-1000uF 6.3-160 DC, pulse DC Ⅲ Ⅳ
Ceramic capacitor 2/7pF-7/25pF 250-500 fine-tuning high-frequency> 1000-10000
Variable capacitor 7pF-1100pF 100 or more low-frequency, high frequency> 500
3. Naming
According to ministry standard (SJ-73) provides that the capacitor of the following four-part name: the first part of the (main name); Part II: (materials); Part III (classification characteristics); fourth part (number) . Significance of their model and the table below.
Table 5 Capacitor type designation
The first part
Part II
Part III
Part IV
With a letter that the Lord calls
Materials with letters
Or letters with digital features
Serial number
Symbolic significance in the symbolic significance of symbolic meaning
C capacitor C
I
O
Y
V
Z
J
B
F
L
S
Q
H
D
A
G
N
T
M
E
Ceramic
Metal Glaze
Glass membrane
Mica
Mica paper
Paper Introduction
Metallized paper
Polystyrene
PTFE
Polyester
Polycarbonate
Film
Paper membrane complex
Aluminum
Tantalum
Metal Electrolysis
Niobium Electrolytic
Titanium electrolysis
Pressure-sensitive
Other materials
T
W
J
X
S
D
M
Y
C
Ferroelectricity
Fine tuning
Metallization
Small-scale
Monolithic
Low
Seal
High pressure
Feed through
Include:
Variety, size, code, temperature, DC voltage, nominal value, tolerances, standards of code.
Table 6 The third part is when representatives of several meanings:
Symbol
Characteristics (type of third part) of the significance of
(Digital) to the mother capacitor Ceramic Capacitor Capacitor Electrolytic Capacitor organic
A wafer non-sealed foil
Two types of non-sealing non-sealed foil
3 laminated seal sealing liquid sintering powder
4 monolithic sintered powder solid seal seal
5 mandrel mandrel
6
7 polarity
8 High High High
9 Special Special
4. Use common sense
Capacitance in the circuit voltage can not actually have to bear more than its voltage value. In the filter circuit, the capacitor AC RMS voltage value of not less than 1.42 times. When using electrolytic capacitors, but also pay attention to positive and negative do not reversed.
Should be used in different circuits of different types of capacitors. Arrangements oscillator circuit can be used mica, high-frequency ceramic capacitors, the choice of paper every other DC-mediated, polyester, mica, electrolytic, ceramic capacitor, electrolytic capacitor filter can be used, bypass the choice of polyester, paper dielectric, ceramic, electrolytic and other capacitors.
Capacitor into the circuit to check it before does not short circuit, open circuit and leakage phenomena, and check its capacitance. When installed, to make the type of capacitor, capacity, pressure and other signs easy to see, for verification.
Second, the general method of detecting capacitor
1. Fixed capacitors for testing.
A detect small capacitance below 10pF. 10pF capacitors due to the following fixed capacity is too small to measure with a multimeter can only check whether there are qualitative leakage, an internal short circuit or breakdown phenomenon. Measurements may make use of multimeter R × 10k block, with two tables document were two random access pin capacitance, resistance should be infinite. If the measured resistance (index to the right swing) is zero, it indicates damage to capacitor leakage or internal breakdown.
B detection 10PF ~ 0 01μF capacitors have charged a fixed phenomenon, which determine the good or bad. Multimeter used R × 1k block. 2 Transistor β values are above 100, and the tunneling current to be small. Optional 3DG6 silicon transistor models such as the composition of composite pipe. Multimeter's red and black table document separately with composite pipe collector emitter e and c phase. As the composite triode amplification, the measured charging and discharging of capacitors to be enlarged, so multimeter index put rate increase, which made it easy observation. It should be noted: In the test operation, especially in the smaller capacity of the capacitance measured when the measured capacitance pin to repeatedly swap contacts A, B two points in order to clearly see the multimeter indicators swing. C 0 01μF or more for a fixed capacitance, the R × 10k multimeter can be used directly to test block capacitor charging process and whether within or without short-circuit or leakage, and can swing to the right under the index range size to estimate the capacitances.
2. Electrolytic capacitor testing
A because the electrolytic capacitor is much greater than the average fixed capacitor, so measurements should be suitable for use in different capacity range. Experience, under normal circumstances, 1 ~ 47μF capacitor between, can be R × 1k block measurement, greater than 47μF capacitance measurement can be R × 100 block.
B the multimeter red table document connected with negative, positive black table document access in the new to the moment, multimeter index that is greater skewness to the right deflection (for the same power block, the greater the capacity, the greater the swing), then gradually left turn, until the stop at a certain location. At this point the resistance is positive electrolytic capacitor leakage resistance, this value is slightly larger than the reverse leakage resistance. Actual experience shows that the leakage resistance of electrolytic capacitors should generally be in the hundreds of kΩ or more, otherwise, will not work. In the test, if positive, no charge reverse phenomenon, that gauge needles do not move, it indicates the capacity disappeared or internal circuit; If the measured resistance value is small or zero, indicating a large capacitor leakage or breakdown damaged, can not re-use. C for positive and negative signs of unknown electrolytic capacitor can be measured using the above method to determine leakage resistance. The first look at any measure leakage resistance, keep in mind the size, and then exchange the table document a resistance measured again. Two major resistance measurement that is positive then the first method, the black sheet document then is positive, the red sheet document then is negative. D use multimeter power block, to the electrolytic capacitor is used, the reverse charge method, according to the size of swings to the right target, can be estimated from the capacity of electrolytic capacitors.
3. Detection of variable capacitor
A gently rotating shaft, should feel very smooth and should not feel tight and sometimes loose even when the cable wiring. Will contain the axial front, back, up, down, left, right, etc. to promote in every direction, the shaft should not be loose phenomenon. B rotating shaft with one hand, one hand moving film set light touch the outer edge, should not feel any loosening. Poor contact between the shaft and the moving film variable capacitors, can not continue to use. C will be placed in R × 10k Multimeter block, a hand to pick the two tables document are dynamic and variable capacitor chips and fixed terminal piece, one hand slowly rotating the shaft a few back and forth, Multimeter Index should be fixed at the infinity position. In the rotating shaft of the process, if the targets are sometimes point to zero, which evidences that exist between films and short films set point; if you encounter a particular point of view, multimeter reading is not infinite but have certain resistance, indicating variable capacitor moving between film and the stator leakage phenomenon.